JP4840960B2 - How to prevent solder bath erosion - Google Patents

Description

  The present invention relates to an erosion prevention method and an erosion prevention device for preventing erosion of a solder bath caused by lead-free solder.

  In recent years, lead-free solders are rapidly spreading from the viewpoint of preventing environmental contamination of lead. While this lead-free solder is useful for environmental protection, it also has problems such as a higher melting point and inferior solder wettability than conventional tin-lead eutectic solder.

  On the other hand, with the use of lead-free solder, there has also been a situation where the solder bath containing molten solder is eroded violently. The reason for this is that the use of lead-free solder increases the percentage of tin, increases the temperature of the molten solder, and uses a strong flux, resulting in the progress of erosion of stainless steel. It has been.

  The solder tank which prevents the erosion accompanying the use of such lead-free solder is disclosed in Patent Documents 1 and 2 below. This solder bath covers all stainless steel surfaces in contact with the molten solder with titanium or nitride.

JP 2002-28778 A JP 2004-141914 A

  However, the techniques disclosed in Patent Documents 1 and 2 have the following problems. First, since the stainless steel surface is only temporarily moved away from the molten solder, the solder bath is eroded when there is no titanium or nitride. In other words, since the true cause has not been investigated, it is not a fundamental solution. Second, it is difficult to apply to existing solder baths. This is because the solder bath must be manufactured using stainless steel whose surface is previously covered with titanium or nitride.

  Accordingly, an object of the present invention is to provide an erosion prevention method and an erosion prevention apparatus that can be applied to an existing solder bath as well as aiming for a solution corresponding to the true cause of the erosion of the solder bath.

  As a result of repeated studies on solder bath erosion by lead-free solder, the present inventor has found that arsenic contained in lead-free solder is involved. That is, arsenic contained in lead-free solder reacts with chromium contained in stainless steel. This is probably because chromium has a strong affinity for arsenic. Specifically, for some reason, the oxide film on the stainless steel surface is destroyed, and arsenic collects and reacts with chromium to form a compound, which prevents the oxide film on the stainless steel surface from repairing. It is thought that the stainless steel that became eroded by tin. That is, the erosion of stainless steel by tin is accelerated by arsenic. This became clear as a result of two-dimensional elemental analysis of the eroded section of stainless steel by energy dispersive X-ray spectroscopy (EDS).

  Arsenic contained in the lead-free solder is supplied from the printed wiring board in the process of soldering the printed wiring board in the solder bath. In the production process of a printed wiring board, a copper plating solution to which arsenic is added in order to enhance the adhesion between the base material and the copper foil is generally used. For this reason, arsenic remains on the surface of the printed wiring board, and this arsenic is washed away with molten solder during soldering and supplied into the molten solder. Therefore, the amount of arsenic contained in the lead-free solder is almost zero in a new product, but increases as a recycled product.

  The reason why erosion of the solder bath by arsenic did not become a problem in conventional tin-lead eutectic solder has not been clarified at present. Presumably, as described above, the ratio of tin was low, the temperature of the molten solder was low, and the action of the flux was weak.

The present invention has been made based on such knowledge. That is, the method for preventing erosion according to the present invention is to remove arsenic contained in molten solder in a solder bath in which molten steel is contained and stainless steel is used in a portion in contact with molten solder. The For example, by oxidizing the arsenic contained in the molten solder, remove arsenic from molten solder.

  As described above, the erosion of the solder bath is remarkably accelerated by the reaction of arsenic contained in the molten solder with chromium contained in the stainless steel. Here, when arsenic contained in the molten solder is oxidized, arsenic oxide is generated, which floats or precipitates in the molten solder. As a result, arsenic that reacts with the stainless steel in the solder bath is eliminated, and erosion of the solder bath is prevented. In other words, active arsenic is converted to inactive arsenic. Since this erosion prevention method may be applied to molten solder, it can also be applied to existing solder baths. In a normal solder bath, solder oxide is generated when the molten solder is oxidized, and this solder oxide is collected and discarded. At this time, arsenic oxide is also collected and discarded together with the solder oxide. In addition, oxidizing arsenic also has an effect of regenerating the oxide film of stainless steel, so it is more effective in preventing erosion of the solder bath.

To oxidize the arsenic contained in the molten solder, we supply a gas containing oxygen in molten solder. The gas containing the oxygen, for example, Ru air der. The use of air will most simplify the equipment compared to the use of other gases.

  Further, when the molten solder is lead-free solder, erosion of the solder bath is remarkable, which is the most effective (claim 5). Examples of the lead-free solder include Sn-Ag, Sn-Ag-Bi, Sn-Ag-Cu, and Sn-Zn-Bi.

Furthermore, the time the solder bath is not used for soldering, Ru to oxidize the arsenic contained in the molten solder. Otherwise, when arsenic is oxidized, part of the molten solder is also oxidized, thereby reducing the soldering quality.

The erosion prevention apparatus according to the present invention uses the erosion prevention method according to the present invention and includes an arsenic removing means. The arsenic removal means for the solder bath stainless steel is used in a portion in contact with the molten solder accommodates the molten solder, remove arsenic contained in the molten solder. The arsenic removal means is arsenic oxidation means. The arsenic oxidation means, by oxidizing the arsenic contained in the molten solder, you remove arsenic from molten solder. Arsenic oxidation means, by supplying a gas containing oxygen into the molten solder, Ru oxygen supply means der to oxidize the arsenic contained in the molten solder.

Stated one example, the oxygen supply means, Ru der those having a hollow body outlet is formed for blowing air installed in the molten solder, a pump for feeding air to the hollow body. Air is pushed into the hollow body by a pump and discharged from the blowout port into the molten solder. In the molten solder, air floats due to specific gravity, and oxygen contained in the air reacts with arsenic contained in the molten solder to generate arsenic oxide.

According to erosion prevention method and apparatus according to the present invention, by removing by oxidation the arsenic contained in the molten solder, since there is no arsenic to react with stainless steel solder bath can be prevented erosion of the solder bath. That is, since the true cause of the erosion of the solder bath was determined to be arsenic contained in the molten solder, an accurate solution can be achieved. Moreover, since this erosion prevention method should just be performed to molten solder, or this erosion prevention apparatus should just be provided in molten solder, it can be applied also to the existing solder tank. In particular, oxidizing and removing arsenic has the effect of regenerating the stainless steel oxide film, which is more effective in preventing corrosion of the solder bath. Furthermore, by oxidizing the arsenic contained in the molten solder during the time when the solder bath is not used for soldering, the quality deterioration of the soldering due to oxidation of a part of the molten solder when arsenic is oxidized is suppressed. be able to.

  Hereinafter, embodiments of an erosion prevention apparatus according to the present invention will be described in detail with reference to the drawings. In addition, the erosion prevention method according to the present invention will be described together with the description of this embodiment.

  FIG. 1 shows a first embodiment of an erosion prevention device according to the present invention, FIG. 1 [1] is a schematic cross-sectional view of the entire soldering device, and FIG. 1 [2] is an enlarged cross section of a part of the erosion prevention device. FIG. Hereinafter, description will be given based on this drawing.

  The soldering device 10 is a dipping type equipped with a solder bath 11 and an erosion prevention device 12. The solder tank 11 contains the molten solder S and is entirely made of stainless steel including a portion that contacts the molten solder S. In addition, the solder bath 11 includes a heater 13. That is, the surface of the heater 13 is also made of stainless steel. Note that the soldering apparatus 10 is provided with a transport mechanism for the printed wiring board P (not shown). The molten solder S is a lead-free solder.

  The erosion prevention device 12 is for preventing the erosion of the solder bath 11 caused by arsenic contained in the molten solder S, and is provided with a pipe 122 provided in the molten solder S and formed with an outlet 121 for blowing out air A. , And a pump 123 for feeding air A into the pipe 122. The pipe 122 is made of, for example, stainless steel, and a plurality of air outlets 121 are formed in a portion installed on the bottom wall side in the solder bath 11.

  Next, the operation of the erosion prevention device 12 will be described. First, the operation of the soldering apparatus 10 will be described. The lead-free solder is heated to a melting point or higher by the heater 13 in the solder bath 11 to become a molten solder S. Here, the printed wiring board P is soldered by immersing the back side of the printed wiring board P on which the electronic component is placed in the molten solder S. At this time, arsenic remaining on the surface of the printed wiring board P is washed away by the molten solder S and accumulated in the molten solder S. Conventionally, this arsenic reacts with chromium contained in the stainless steel of the solder bath 11 to generate a compound, so that the erosion of the solder bath 11 is remarkably accelerated. Specifically, for some reason, the oxide film on the stainless steel surface is destroyed, and arsenic collects and reacts with chromium to form a compound, which prevents the oxide film on the stainless steel surface from repairing. It is thought that the stainless steel that became was eroded by tin.

On the other hand, in this embodiment, the erosion prevention device 12 oxidizes and removes arsenic contained in the molten solder S. That is, the air A is pushed into the pipe 122 by the pump 123 and is discharged into the molten solder S from the air outlet 121. In the molten solder S, the air A floats due to the specific gravity. At that time, oxygen contained in the air A and arsenic contained in the molten solder S react to generate arsenic oxide. As a result, arsenic that reacts with the stainless steel in the solder bath 11 disappears, so that the corrosion of the solder bath 11 is prevented. Moreover, since the corrosion prevention apparatus 12 should just provide the pipe 122 in the molten solder S, it is applicable also to the existing solder tank.

  Generally, in the solder tank 11, solder oxide (referred to as “dross”) is generated by the oxidation of the molten solder S, and this solder oxide is collected and discarded. At this time, arsenic oxide is also collected and discarded together with the solder oxide. Further, arsenic contained in the molten solder S is oxidized during the time when the solder bath 11 is not used for soldering. Otherwise, when the arsenic is oxidized, a part of the molten solder S is also oxidized, so that the soldering quality is deteriorated. Therefore, the soldering process is a procedure of arsenic oxidation → dross disposal → soldering.

  In addition, you may change the quantity and shape of the pipe 122, and the quantity and shape of the blower outlet 121 as needed. Further, air A may be introduced from existing air piping instead of the pump 123.

  FIG. 2 shows a second embodiment of the erosion prevention device according to the present invention, FIG. 2 [1] is a schematic sectional view of the entire soldering device, and FIG. 2 [2] is an enlarged cross section of a part of the erosion prevention device. FIG. Hereinafter, description will be given based on this drawing. However, the description of the same parts as those in the first embodiment is omitted or simplified.

  The soldering apparatus 20 of the present embodiment is a jet type equipped with a solder bath 21 and an erosion prevention apparatus 22. The solder tank 21 contains the molten solder S and is entirely made of stainless steel including a portion that contacts the molten solder S. The solder bath 21 includes a heater 23, a shaft 24, fins 25, a duct 26, rectifying perforated plates 27a and 27b, a nozzle 28, and the like. That is, the surface of the heater 23, the shaft 24, the fin 25, the duct 26, the rectifying porous plates 27a and 27b, and the nozzle 28 are also made of stainless steel. In addition, although not shown in figure, the soldering apparatus 20 is provided with the conveyance mechanism of the printed wiring board P. As shown in FIG. The molten solder S is a lead-free solder. The rectifying perforated plates 27 a and 27 b function to make the flow of the molten solder S uniform and send it to the nozzle 28.

  The erosion prevention device 22 is for preventing erosion of the solder bath 21 caused by arsenic contained in the molten solder S, and is provided with a pipe 222 provided in the molten solder S and formed with an outlet 221 for blowing out air A. And a pump 223 that feeds air A into the pipe 222. The pipe 222 is made of, for example, stainless steel, and a large number of air outlets 221 are formed in a portion installed on the side wall side in the solder bath 21.

  Next, the operation of the erosion prevention device 22 will be described. First, the operation of the soldering apparatus 20 will be described. The lead-free solder is heated to the melting point or higher by the heater 23 in the solder bath 21 to become a molten solder S. The shaft 24 rotates the stirring fins 25 by transmitting power from a motor (not shown). The molten solder S sent into the duct 26 by the fins 25 passes through the rectifying porous plates 27a and 27b and is ejected from the nozzle 28. Here, the printed wiring board P is soldered by bringing the back side of the printed wiring board P on which the electronic component is placed into contact with the molten solder S ejected. At this time, arsenic remaining on the surface of the printed wiring board P is washed away by the molten solder S and accumulated in the molten solder S. Conventionally, this arsenic reacts with chromium contained in the stainless steel of the solder bath 21 to generate chromium arsenide, so that erosion of the solder bath 21 has been remarkably accelerated. In the jet type soldering apparatus 20, the molten solder S is forcibly agitated so that it is greatly eroded by the shaft 24, the fin 25, the duct 26, the rectifying perforated plates 27a and 27b, the nozzle 28, and the like. Is done.

On the other hand, in this embodiment, the erosion prevention device 22 oxidizes and removes arsenic contained in the molten solder S. That is, air A is pushed into the pipe 222 using the pump 223, and the air A is discharged into the molten solder S from the outlet 221 to generate arsenic oxide. At this time, in order to efficiently mix the air A into the molten solder S, it is desirable to circulate the molten solder S. As a result, arsenic that reacts with the stainless steel in the solder bath 21 is eliminated, and therefore the erosion of the solder bath 21 is prevented. Moreover, since the corrosion prevention apparatus 22 should just provide the pipe 222 in the molten solder S, it is applicable also to the existing solder tank. The soldering process in the present embodiment is a procedure of arsenic oxidation → dross while discarding, or arsenic oxidation → dross disposal → soldering.

  FIG. 3 is an explanatory view showing another embodiment of the erosion prevention apparatus according to the present invention, in which FIG. 3 [1] is a first example and FIG. 3 [2] is a second example. Hereinafter, description will be given based on this drawing.

  In the first example, when the molten solder S ejected from the nozzle 28 is dropped onto the liquid surface of the molten solder S in the jet type soldering apparatus shown in FIG. 2, the air A is mixed into the molten solder S. It is what I did. In the second example, the air A is mixed into the molten solder S by rotating the stirring impeller 30 so as to cut the liquid level of the molten solder S.

  Needless to say, the present invention is not limited to the above embodiments. For example, the entire solder bath to which the present invention is applied need not be made of stainless steel, and it is sufficient that stainless steel is used even in a portion that contacts the molten solder.

1 shows a first embodiment of an erosion prevention device according to the present invention, FIG. 1 [1] is a schematic sectional view of the entire soldering device, and FIG. 1 [2] is an enlarged sectional view of a part of the erosion prevention device. . FIG. 2 [1] is a schematic cross-sectional view of the entire soldering apparatus, and FIG. 2 [2] is an enlarged cross-sectional view of a part of the erosion prevention apparatus. . It is explanatory drawing which shows other embodiment of the erosion prevention apparatus which concerns on this invention, FIG. 3 [1] is a 1st example and FIG. 3 [2] is a 2nd example.

Explanation of symbols

10 Soldering device (immersion type)
11 Solder bath (immersion type)
12, 22 Erosion prevention device (oxygen supply means, arsenic oxidation means, arsenic removal means)
121, 221 Air outlet 122, 222 Pipe (hollow body)
123,223 Pump 20 Soldering device (jet type)
21 Solder bath (jet type)
S Molten solder (lead-free solder)
P Printed wiring board

Claims (2)

With respect to a solder bath in which stainless steel is used for a portion that contacts molten solder and contains molten solder made of lead-free solder,
Oxidizes arsenic contained in the molten solder by supplying a gas containing oxygen into the molten solder at a time when the solder bath is not used for soldering;
A method for preventing erosion of a solder bath. The gas containing oxygen is air;
The method for preventing erosion of a solder bath according to claim 1.

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